Multiple-entry hot-mix asphalt manufacturing system and method

ABSTRACT

A hot-mix asphalt manufacturing system for recycled asphalt coated aggregate (RAP) has a rotary dryer and burner operable to heat the dryer to create a maximum gas temperature at a location between first and second ends of the dryer. A first inlet is upstream and a second inlet is downstream of the maximum temperature. A first coarse aggregate is introduced through the first inlet, fine RAP is introduced through the second inlet, and the aggregates are heated and mixed forming a mixture outputted at an outlet. For 100% RAP processes, the first and second aggregates can consist of RAP. For less than 100% RAP processes, virgin aggregate can be introduced through the first inlet, located adjacent the first end of the rotary dryer, and a third inlet can be located between the maximum temperature and the first inlet, with fine and coarse RAP introduced through the second and third inlets.

FIELD OF THE INVENTION

The present teachings relate generally to asphalt manufacturing and,more specifically, to hot-mix manufacturing using recycled asphaltcoated aggregate.

BACKGROUND OF THE INVENTION

The asphalt manufacturing industry has in the past used recycled asphaltcoated aggregate (commonly called RAP) in place of or in combinationwith virgin aggregates. However, doing so introduces a number ofproblems. For example, undesirable hydrocarbon emissions can be createdwhen exposing the asphalt coated RAP to hot combustion gases.

Strategies to heat RAP without creating excessive hydrocarbon emissionshave included microwave heating, indirect heating, and most commonlymixing with superheated virgin aggregates. However, such strategiessuffer unnecessary restrictions on capacity to heat the RAP and,consequently, limit maximum recycled content or production rate.

U.S. Pat. No. 6,478,461, the content of which is incorporated byreference in its entirety, was previously issued to the inventor anddiscloses a transportable hot-mix asphalt manufacturing and pollutioncontrol system for use with recycled asphalt coated aggregate (RAP). Thesystem disclosed in the '461 patent utilizes a single entry point foraggregate.

U.S. Pat. No. 3,999,743 to Mendenhall, the content of which isincorporated by reference in its entirety, discloses anasphalt-aggregate recycling process using center entry in a rotary dryerto limit radiant and/or convective heat transfer. The system disclosedin the '743 patent teaches a parallel flow dryer with coarse, moredifficult to heat material introduced closer to the flame and fineparticles furthest away.

The techniques used in the prior art suffer a number of limitations,including inefficiencies realized when using higher percentages of RAPaggregate. Therefore, it would be beneficial to have a superior systemand method for hot-mix asphalt manufacturing.

SUMMARY OF THE INVENTION

The needs set forth herein as well as further and other needs andadvantages are addressed by the present embodiments, which illustratesolutions and advantages described below.

Traditionally, the use of RAP by many asphalt manufacturers has beenlimited to around 40% of mixture. However, the present teachings enablethe efficient use of RAP up to 100%. A system according to the presentteachings provides a number of other benefits beyond the increased useof recycled materials. For example, pollution control is also improvedas less heat may be used to heat the RAP and airborne particulates maybe substantially reduced. These benefits may result in a simplifiedpollution control system.

In one embodiment, the system according to the present teachingsincludes a multiple entry rotary dryer having one or more “center”entries for introducing recycled asphalt coated aggregate (RAP). Thesystem may include a counter flow heating apparatus that provides aparabolic temperature profile in the rotary dryer. The temperatureprofile may be used to determine desirable locations for introducingcoarse and fine aggregate. For example, coarse RAP aggregate may beintroduced before (i.e., upstream of) the peak temperature in the rotarydryer whereas fine RAP aggregate may be introduced after (i.e.,downstream of) the peak temperature relative to direction of materialflow.

Other embodiments of the system and method are described in detail belowand are also part of the present teachings.

For a better understanding of the present embodiments, together withother and further aspects thereof, reference is made to the accompanyingdrawings and detailed description, and its scope will be pointed out inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a rotary dryer accordingto one embodiment of the present teachings.

FIG. 2 is a temperature profile of the rotary dryer according to thesystem of FIG. 1.

FIGS. 3A-B are schematic views of a center entry collar and bucket foruse with the system of FIG. 1.

FIG. 4 is a perspective view of the combustion zone inside a dryerhaving insulator flights in area of peak air temperature.

FIG. 5 is a side elevation cross-sectional view of a dryer havinginsulator flights at zone of peak air temperature.

FIG. 6 is a plan view of a pair of insulator flights.

FIGS. 7 and 8 are perspective views from upstream and downstream ends ofa combustion zone inside a driver having insulator flights in the areaof peak air temperature and having a dam at a downstream end of thezone.

FIG. 9 is a schematic cross-sectional view of a rotary dryer accordingto an embodiment of the present teachings showing a unitary pollutioncontrol system.

DETAILED DESCRIPTION OF THE INVENTION

The present teachings are described more fully hereinafter withreference to the accompanying drawings, in which the present embodimentsare shown. The following description is presented for illustrativepurposes only and the present teachings should not be limited to theseembodiments.

For purposes of explanation and not limitation, specific details are setforth in order to provide a thorough understanding. In other instances,detailed descriptions of well-known devices and methods are omitted soas not to obscure the description with unnecessary detail.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated. The use of “first”, “second” etc.for different features/components of the present disclosure are onlyintended to distinguish the features/components from other similarfeatures/components and not to impart any order or hierarchy to thefeatures/components.

The present teachings can be used to increase the use of recycledasphalt content in any number of different systems. For example, directfired counter flow (CF) rotary dryers, continuous mix plants havingseparate mixers after dryers, batch mix plants, and CF dryers withexternal combustion sources, although not limited thereto, may benefitfrom the present teachings. A continuous mix plant is a plant whereaggregates are coated with an asphalt binder and other liquid additivesin a rotary dryer after drying. In contrast, a batch mix plant may storeheated aggregates and then mix discrete batches with an asphalt binderand liquid additives in a space separate from the dryer. Althoughspecific embodiments are disclosed, one skilled in the art wouldappreciate that the present teachings are not limited thereto.

RAP is typically recovered from existing road surfaces and other areasby a milling process, or another suitable process, and is broken apartinto constituent particles for processing and reuse. RAP may beseparated based on particle size that are commonly characterized in twoclasses: fine and coarse aggregate, which can be distinguished based ontheir relative sizes. The classification of aggregates as fine or coarsein the asphalt industry is generally known. It is generally acceptedthat “sands,” either manufactured or natural, are fine aggregates while“stones” are coarse aggregates. For example, fine aggregates may includethose that pass through a #4-#8 sieve (e.g., 0.187 to 0.0937 inch sieveopening), where coarse aggregates are larger and may be retained on thatsieve.

Fine and coarse aggregates may also be distinguished by differences intheir surface area to mass ratios. Fine aggregates may have high surfaceareas relative to their mass (e.g., a high specific surface area),whereas coarse aggregates may have small surface area to mass ratios(e.g., a low specific surface area). Therefore, fine aggregates may havehigher heat transfer rates per unit weight relative to coarse aggregatesince heat transfer is proportional to surface area. Similarly, thetemperature of fine aggregates may increase more quickly than coarseaggregates at a given differential temperature since fine aggregateshave a smaller mass and temperature increase is inversely proportionalto particle mass.

It has been found that fine RAP aggregate may heat more rapidly from hotcombustion gases than coarse RAP due to fine RAP's large surface arearatio. In a system where fine and coarse aggregate are introducedtogether, fine aggregates tend to give up heat to coarse aggregate asthe two lay commingled in the bottom of a dryer. This exchange maycontinue as the dryer rotates and the aggregate progresses down thedryer from inlet to discharge outlet. However, this may causeundesirable clumping and adhesion of fine aggregate on the dryer due tothe asphalt binder coating the fine aggregate being activated duringheating and then being cooled by the relatively colder coarse aggregateto a point where it becomes tacky, causing clumping.

To overcome the above problem, it has been found that it is beneficialto have separate feed locations for fine and coarse RAP when a higherrecycled content is desired (e.g., in rotary dryers on batch orcontinuous mix drum plants). This may be especially so in counter flowdryers where the heat source (e.g., burner) is nearer to the dischargepoint and directs heat toward the colder inlet end of the dryer.

It has been found that, since coarse RAP requires more time to heat itcan be introduced earlier in a counter flow rotary dryer withoutsignificant increase in hydrocarbon emissions. The large thermal mass ofcoarse aggregate serves to moderate the temperature increase of theaggregate. Consequently, coarse RAP can be exposed longer to hotter gastemperatures (and the radiant energy of a burner flame) than fine RAPwithout visible emissions or increasing hydrocarbon emissions aboveother asphalt manufacturing processes.

Further, it has been found that fine RAP's high specific surface areaenables it to be dried and heated in significantly less time than coarseaggregate. Therefore, it can be introduced behind (i.e., downstream of)the peak temperature profile yet still release surface moisture andreach adequate discharge temperature at high feed rates.

As will be discussed in more detail below, rotary dryers may have anumber of distinct zones, depending on plant type. Such zones may beidentified by their temperature profiles and/or function, although notlimited thereto. A “drying zone” may be optimized to transfer heat fromcombustion gases to raw material by means of convective transfer to fineaggregate, and conductive transfer from the fine aggregate to the coarseaggregate.

A “combustion zone” may be optimized to facilitate complete combustionof fuels in a space shared with aggregates. To protect the dryer,insulator flights (discussed below) may be provided in the combustionzone (and other zones) to insulate the dryer shell and to convertradiant energy to thermal that is then transferred to the aggregateprior to exiting the combustion zone.

Finally, a “mixing zone” may be downstream from the drying andcombustions zones to facilitate mixing asphalt cement binder (or othersupplemental ingredients) with the heated aggregate.

Although three zones are discussed herein, the present teachings are notlimited thereto, and one skilled in the art would appreciate that asystem could utilize more or fewer zones without deviating from theseteachings.

In one embodiment, the air temperature profile in the combustion zonemay be roughly parabolic, going from the material discharge temperature(e.g., ˜300 F) behind the flame (in a counter-flow dryer) to a maximumtemperature at a midpoint of the combustion zone along the dryer length(e.g., ˜1400 F-2000 F) and then gradually back down to lower inlettemperature (e.g., ˜280 F) at the first inlet. Fine RAP may be introduceafter the maximum temperature point while coarse RAP may be introducedat a point where it will pass through that maximum. Coarse RAP may alsobe introduced in the drying zone, but this may result in increasedhydrocarbon emissions that potentially could require treatment to complywith air pollution regulations.

Referring now to FIG. 1, shown is a schematic cross-sectional view of arotary dryer according to one embodiment of the present teachings.

As shown, a hot-mix asphalt manufacturing system may comprise a rotarydryer 100 adapted to receive ingredients of hot-mix asphalt and toperform a drying and heating process on such ingredients, although notlimited thereto.

Preferably, the rotary dryer 100 is a counter-flow rotary dryer. Theterm “counter-flow” is understood to mean that the materials being driedin the rotary dryer 100 generally have a flow stream (i.e., areconveyed) in one direction, whereas the hot combustion gases and/orby-products of the drying process flow in an opposite direction. Asshown, the rotary dryer 100 may include a burner 102 (or other heatsource) and a rotatable drum 104 having a first end 106, which iselevated, and a second end 108, which is lower than and opposite thefirst end 106. The burner may provide a flame with a conical shape,although not limited thereto. Material may be heated with hot gasestraveling upstream in a direction opposed to the material flow stream.The rotary dryer 100 may include a drying zone 120, combustion zone 122and mixing zone 118, discussed further below.

In an alternative embodiment, a separate mixing/coater may be used. Thisincludes batch type plants having a separate batch tower and pugmillmixer that combine aggregates with fresh asphalt. A separate externalcontinuous coater may be either a paddle type mixer or rotating drum.

An external combustion source may also be used. In this case, the flameis removed from the rotary dryer. Combustion may take place in astationary space typically lined with refractory or similar heatresistant materials where radiant energy is converted into thermalenergy (e.g., hot gases) before entering the rotary dryer.

A first inlet 110 for “new” aggregate (e.g., fresh or virgin aggregate)may be located at or adjacent the first (elevated) end 106 of therotatable drum 104. What is meant by “new” or virgin aggregate isaggregate that has not been (or essentially has not been) reclaimed orrecycled from a previous asphalt mixture, for example from an existingroad surface. A second inlet 114 for fine RAP may be located at anintermediate position between the first inlet 110 and the second end108. A third inlet 112 may be used for coarse RAP and may be located atan intermediate position between the first inlet 110 and the secondinlet 114. Specifically, the third inlet 112 can be downstream of thefirst inlet 110 and upstream of the second inlet 114. A discharge outlet116 for the hot-mix asphalt manufactured by the rotary dryer 100 can belocated at or near the second end 108. One skilled in the art wouldappreciate that this configuration is exemplary and the presentteachings are not limited thereto.

For hot-mix asphalt processes using at or near 100% recycled asphaltcoated aggregates (RAP) (or when virgin aggregates are commingled withcoarse RAP), the aggregate may be introduced through the first inlet 110and fine RAP may be introduced through the second inlet 114, in whichcase the third inlet 112 could be unused or omitted. However, it may bepreferable to have the first, second and third inlets 110, 114, 112 forconventional processes using less than 100% RAP so new material may beintroduced at the first inlet 110, with fine and coarse RAP introducedat the second and third inlets 114, 112, respectively.

In a system using less than 100% RAP, fresh (virgin) primary aggregatesmay be brought to the first inlet 110 and introduced into the rotatabledrum 104 using a conventional conveyor system (e.g., a belt-typeconveyor). The fine and coarse recycled ingredients may be introducedthrough the second and third inlets 114 and 112, respectively, by a RAPcollar or another suitable method. For process using 100% RAP and/orless than 100% RAP, the coarse and fine aggregates may be about 64% andabout 36% of the total RAP content, respectively, although not limitedthereto.

Supplemental ingredients (e.g., additives) can be introduced into themixing zone 118 to be mixed with the coarse and fine aggregate afterthey have substantially completed drying and heating in a drying zone120 and combustion zone 122, although not limited thereto. Supplementalingredients may include, for example, fresh or recycled asphalt cement,recycling agents, fibers, polymers, fillers, and/or combinationsthereof, although not limited thereto.

In operation, the primary ingredients of the hot-mix asphalt may bereceived through the inlets 110, 112, 114 for passage through therotatable drum 104 toward the second end 108. At the same time,combustion gases from the burner 102 may flow substantially from theburner 102 toward the first end 106 to heat and dry the ingredients.Downstream of the mixing zone 118 (with respect to ingredient flow), thehot-mix asphalt manufactured by the rotary dryer 100 may be allowed todrop through the outlet 116 and onto a hot-mix conveyor system.

Referring now to FIG. 2, shown is a temperature profile 150 of a rotarydryer 100 according to one embodiment of the present teachings. As shownby the temperature profile 150, three zones, namely, a drying zone 120,combustion zone 122, and mixing zone 118 may be identified by theirrelative positions and temperatures, although not limited thereto. Forexample, as heat leaves the burner 102 it may produce a parabolic airtemperature profile 150 in the rotary dryer 100, with the highest (peak)temperature found in a middle of the combustion zone 122. Thetemperatures shown in FIG. 2 are exemplary in nature and not limiting.

The temperature profile 150 may be used to determine preferablelocations for the inlets 112, 114 (shown in FIG. 1). Virgin material maybe introduced at the furthest upstream point in the material flowstream, for example, at the first inlet 110 (shown in FIG. 1). CoarseRAP may preferably be introduced downstream of the first inlet 110 andupstream of the peak temperature gradient in the dryer, in or adjacentto the upstream end of the combustion zone, for example, at the thirdinlet 112 (shown in FIG. 1). Fine RAP may then preferably be introduceddownstream of the peak temperature gradient in the dryer, in or adjacenta downstream end of the combustion zone, for example, at the secondinlet 114 (shown in FIG. 1), which is downstream of the third inlet 112.

In one embodiment, the second inlet 114 may be roughly 4 feet upstreamfrom an end 103 of the tubular extension 105 of the burner 102 (shown inFIG. 1) anchoring the flame, which may be about 10 feet from thedischarge outlet 116. The second inlet 114 may be within the combustionzone (as shown), outside of the combustion zone (e.g., in the mixingzone) or even as a separate material feed to the batch mixer, althoughnot limited thereto. The third inlet 112 may be roughly 6 to 10 feetupstream from the end 103 of the tubular extension 105 of the burner102, and the first inlet 110 may be about 24 feet from the end 103 ofthe tubular extension 105, for a dyer having a length of about 34 feet.Asphalt cement and/or supplemental additives may be introduced about 6to 8 feet upstream from material discharge outlet 116 for a unifieddryer/mixer as shown, although not limited thereto. Alternatively oradditionally, it may be added at the batch mixer or part of externalcoater.

New material (e.g., for conventional <100% RAP processes) is preferablyintroduced at the first inlet 110 and, by the time the new materialreaches the coarse RAP entry point, for example third inlet 112, the newmaterial may preferably be at a desired mix discharge temperature thatcan range from 250-330 F, although not limited thereto. By the time thecoarse RAP/new material mix (or coarse RAP for 100% RAP processes, etc.)reaches the fine RAP entry point, the coarse RAP/new material maypreferably be at a desired mix discharge temperature that can range from250-330 F, although not limited thereto. The temperature rangesdisclosed herein are exemplary in nature and not limiting.

Where RAP includes one or more intermediate gradation(s) of aggregatebetween fine and coarse RAP (for example, where RAP includes fine,medium and coarse gradations of aggregate), the intermediategradations(s) of RAP can be introduced through the fine and/or coarseRAP inlets, or through additional inlet(s), specific to the intermediategradations(s) of RAP, which may be located between the inlets for fineand coarse RAP.

Benefits of the multiple entry system include the ability to producemixes where all or a majority of aggregate is provided by a RAP feed.Introducing coarse RAP upstream of the peak temperature in the dryer anddirectly heating the coarse RAP in the combustion zone 122 may reducetemperature requirements of fresh aggregate that otherwise must besuperheated (e.g., 100 to 500 degrees F. above desired dischargetemperature). Increased usage of RAP, and specifically increased usageof RAP fines, reduces the requirement for new (virgin) fine materialcontaining ultra-fine material (e.g., minus 70 micron) that is easilymade airborne and carried into a bag house. Ultra-fine material in RAPmay be bound by a RAP binder to larger particles and not easily madeairborne. Thus, pollution control may be simplified.

More thorough heating and drying of RAP aggregates results from longertime in the dryer. Internal moisture in the center of the aggregate isreleased in the dryer. This is different than that shown in the priorart, where interior moisture remains in high RAP mixes which then tendto cool after discharge due to evaporation of the interior moisture.According to the present teachings, more gradual heating of RAPaggregates results because RAP lays in the bottom of the dryer withaggregate close to mix discharge temperature. This also results in lessdamage to the RAP binder otherwise caused by exposure to superheatedaggregates. For example, the prior art requires superheating freshaggregate (e.g., to over 800 F for only 40% recycled content). The RAPbinder can be damaged at these temperatures.

There is better transfer of RAP binder to fresh aggregates using asystem according to the present teachings. Heating in the combustionzone while mixed with fresh aggregate increases mixing energy todistribute the RAP binder evenly. This reduces spatial variations inbinder content between recycled and fresh aggregates.

The use of colder, fine RAP aggregate may be used to cool combustiongases. Also, adding fines separately from coarse aggregate maysignificantly reduce buildup of RAP fines in the dryer. Both fine andcoarse RAP may be heated more thoroughly before being mixed with freshbinder material. In addition, a RAP binder may be better distributedonto fresh uncoated particles reducing spatial variation in bindercontent of finished product, although not limited thereto

The system according to the present teachings is also safer since theprobability of all entry feeds running empty simultaneously is muchlower than for systems described in the prior art where RAP aggregate isintroduced at a single location. Multiple entry feed provides aredundancy so the material in the dryer doesn't overheat. There may beno need to superheat new material (e.g., to 800 F). Excessivehydrocarbon fumes from fresh asphalt binder are created if superheatedaggregate reaches the mixing zone without being cooled by RAP feed.Hydrocarbon fumes create risk of fire in the dryer or bag house whenfumes are ignited as they pass through the combustion zone. This is aproblem in the prior art with high RAP mixes and counter flow dryerswhen the sole RAP feed in a single-feed system is interrupted. Aredundant feed also decreases the risk of fire from ignited hydrocarbonfumes because redundant RAP feeds are less likely to fail in unison.

Temperature of the air stream exiting the dryer also may remain uniformas RAP percentage changes. The prior art suffers significantly higherdryer exit gas temperatures as the percentage of RAP increases and freshaggregate is superheated. Superheating reduces heat transfer efficiencyof the dryer due to lower temperature difference between aggregate andgases. Accordingly, there may be more efficient dryer operationaccording to the present teachings because less heat is lost throughductwork, dryer shell and exit gas temperature.

The present teachings may be used to retrofit conventional asphaltmanufacturing systems to increase RAP use up to 100%. Such systems mayalready have an existing entry for RAP (e.g., a collar) which may beused for RAP, although not limited thereto. Alternatively oradditionally, coarse RAP may be added in the first inlet for 100% RAPprocesses, or for processing using less than 100% RAP, a coarse RAPinlet could also be added in accordance with the present teachings.

In preexisting counter-flow dryers used for RAP processes, a single RAPentry is typically located between the combustion and mixing zones. Toconvert such systems, the retrofit can include shortening the tubularextension 105 of the burner 102 to move the end 103 of the tubularextension (and thus also the combustion zone) downstream such that theexisting RAP entry is in the combustion zone, downstream of the peakdryer temperature, making the system suitable for introduction of fineRAP aggregate according to the present teachings. If required, theasphalt cement/supplemental additives (AC) injection point can be moveddownstream to maintain the AC injection point in a shortened mixingzone. Further, an inlet for coarse RAP can be added in the combustionzone, upstream of the peak dryer temperature, as described herein.

Inlets for introducing fine RAP aggregate and coarse RAP aggregate arediscussed herein. One skilled in the art would appreciate that materialintroduced through the inlet for fine RAP aggregate may be solely fineRAP. Alternatively, the material may be primarily fine RAP or mayconsist essentially of fine RAP. Thus, the material introduced throughthe inlet for fine RAP may include components other than fine RAP, suchas other gradations of RAP aggregate and/or virgin aggregate, processedshingles, or other components. Similarly, material introduced throughthe inlet for coarse RAP aggregate may be solely coarse RAP, oralternatively may consist essentially of or may be primarily coarse RAP,including other gradations of RAP and/or virgin aggregate, or othercomponents.

Referring now to FIGS. 3A-B, shown are schematic views of a collar andbucket for use with the system of FIG. 1. As shown, a special design maybe used for a RAP collar 200 for introducing fines to a dryer. This mayprovide straight transfer from the exterior of the dryer to the interiorperpendicular to the axis of the dryer.

Interior buckets 202 may create a one-way door to keep the aggregate inthe dryer. They may empty onto insulator flights that protect the dryershell from peak temperatures (e.g., +2000 F). Segmented flights may linethe dryer shell at the combustion zone. Aggregates may pass over the topof the insulator flights.

Referring now to FIGS. 4-6, shown is an inside view of a dryer 300having a plurality of insulator flights 310 lining an interior of thedryer shell 320. The insulator flights 310 are designed to shield thedryer shell 320 from heat generated by the heat source (e.g., theburner), and to minimize heat loss to the ambient environment.

The insulator flights 310 can be segmented to allow for individualremoval and replacement as required and can be installed side by sideand end to end, overlapping one to another to completely cover (i.e.,line) the interior of the dryer shell 320, over a potion the interior orthe entire interior. Multiple circumferential bands of insulator flights310 can be arranged in a longitudinally adjacent, closely abuttingarrangement to effectively line an area of the dryer shell 320.

In one embodiment, insulator flights may be installed in the combustionzone of the rotary shell dryer. This is where fuel from the burnercompletes combustion and provides volume for hot gases to expand andfuel access to oxygen. However, insulator flights could be installed inall zones or any particular portions of the dryer, as desired.Installing them throughout the length of the dryer may help protect thedryer from excessive wear and tear caused by aggregate.

Preferably, the insulator flights 310 are formed from steel plates (forexample ⅜″ thick) and are attached to the interior of the dryer shell320 so that they rotate with the dryer. The insulator flights 310 arespaced radially inwardly from the shell 320 of the dryer 300 forming anannular gap 330 between the insulator flights 310 and the shell 320.

Insulation 340, such as ceramic insulation or other suitable insulation,is disposed in, and preferably substantially fills the gap 330. Thepresence of the insulation 340 in the gap 330 serves the insulation andprotective purposes discussed herein, and, in addition, serves toprevent aggregate and other materials from entering the gap 330 betweenthe insulator flights 310 and the dryer shell 320. Thus, the insulation340 may prevent the annular gap 330 between the interior surface of thedryer shell 320 and the insulator flights 310 from filling with fineaggregate, which can negatively impact mix gradation.

The insulation 340 can provide increased thermal efficiency and helpprevent heat transfer to the dryer's outer shell and supportingstructures. However, external insulation (not shown) on the exterior ofthe dryer 300 could also be used for better thermal efficiency. Thus,the use of the insulator flights 310 may also enable the use of anadditional insulation layer outside of the dryer shell 320 to reduceheat loss to the atmosphere without risk of excessive steel temperaturesin the dryer shell 320 (e.g., <600 F) at the combustion zone.

The insulator flights 310 have a substantially rectangular base portion350 which is spaced radially inwardly from the shell 320 of the dryerand which is preferably curved to complement or follow the curvature ofthe dryer shell 320. In particular, when installed, an axis of curvature352 of the base portion 350 is preferably substantially the same as(i.e., substantially collinear with) an axis of curvature of shell 320of the dryer 300. The insulator flights 310, and can have a longitudinallength of about 4 feet and a can have a circumferential width (i.e., arclength) of about 1.5 feet.

The insulator flights 310 have a circumferential overlapping portion 360preferably integrally formed with the base portion 350 and extendingfrom a rotationally downstream longitudinal edge 370 of the base portion360. The circumferential overlapping portion 360 is angled to projectradially inwardly from the base portion 360 sufficiently such that itoverlaps and contacts a radially inward surface of the rotationallydownstream adjacent insulator flight 310. In particular, thecircumferential overlapping portion 360 of the insulator flight 310contacts and overlaps a radially inward surface of the rotationallyupstream longitudinal edge 380 of the adjacent insulator flight 310,forming a substantial seal therebetween. As depicted, all of theinsulator flights 310 overlap as described herein such that theinsulator flights 310 form a substantially circumferentially contiguouslining for the dryer shell 320 such that, during operation and rotationof the dryer 300, material flows over each successive insulator flight310 in a circumferential direction.

The insulator flights 310 also overlap in the longitudinal direction.Preferably, the insulator flights 310 have a longitudinal overlappingportion 390 substantially covering a seam between longitudinallyadjacent insulator flights 310. The longitudinal overlapping portion 390can be fixed (e.g., welded or integral) to a radially inward surface ofone of the adjacent insulator flights 310, for example a longitudinallydownstream edge 400 of a longitudinally upstream insulator flight 310.Thus, in the area in which the insulator flights 310 are present, theycan form a substantially longitudinally contiguous lining for the dryershell 320 so that, during operation and rotation of the dryer 300,material flows over each successive insulator flight 310 in thedirection of the material flow stream in the dryer 300.

The insulator flights 310 are preferably fixed to the dryer shell 320 ina manner that allows substantial thermal expansion and contraction ofthe insulator flights 310 during operation cycles, thereby avoidingsubstantial thermal stress. Preferably, the insulator flights 310 areheld in place by a pair of compression plates 410, 420 bearing on orattached to a radially inward surface of the base portion 350, forexample at longitudinally upstream and downstream portions of therotationally downstream longitudinal edge 370 of the base portion 350.Each compression plate 410, 420 can be mounted on a clip base 430affixed to and projecting radially inwardly from the dryer shell 320.The opposite longitudinal edge of the insulator flights 310,specifically the rotationally upstream longitudinal edge 380, ispreferably indirectly connected to the dryer shell 320 by being trappedor clamped down by the circumferential overlapping portion 360 of therotational upstream adjacent insulator flight 310 as described herein.

Preferably, the insulation 340 disposed in the gap 330 is compressedbetween the insulator flights 310 and the dryer shell 320 and isresilient such that it exerts radially inward pressure on the radiallyoutward surface of the insulator flights 310 to effectively trap eachinsulator flight 310 between the associated compression plates 410, 420and the circumferential overlapping portion 360 of the adjacentinsulator flight.

To construct a system according to the present teachings, the insulation340 may be laid on the inside of the dryer shell 320 in an uncompressedstate and then the insulator flights 310 may be attached to the dryershell 320 over the insulation as discussed herein. During suchinstallation, the insulator flights 310 may compress the insulation 340to a thickness of about 25%-75%, or preferably about 50%, of theuncompressed thickness of the insulation 340. For example, for a gap 330of about 2 inches, insulation 340 having an uncompressed thickness ofabout 2.5 inches to about 8 inches, or preferably about 4 inches, wouldbe suitable.

The insulation 340 may be dense mineral insulation, preferably ceramicfiber, which is able to withstand the high temperatures in the dyer 300and in particular in the combustion zone of the dryer 300.

The dyer 300 can include a plurality of lifting flights 500 to enhancemixing and heating of materials within the dryer 300. The lifting fights500 can be affixed to the base portions 350 of the insulating flights310 and can be oriented in a longitudinal direction as shown. Thelifting flights 500 can have a stem portion 510 affixed to andprojecting radially inwardly from the insulator flight 510, and can havea hook portion 520 extending circumferentially in the direction ofrotation of the dryer shell 320 from a radially inward end of the stemportion 510, forming a substantially-L shape.

The insulator flights 310 and lifting flights 500 are preferablydisposed at regular circumferential (i.e., angular) intervals, forexample in about 9 intervals (or about every 40 degrees) for smalldiameter dryers, or one per insulator flight segment.

The lifting flights 500 can be tapered such that they decrease in sizein a direction toward the heat source for the dryer 300, to graduallyreduce the amount of material that the lifting flights 500 carry inareas closer to the flame initiation (e.g., the end 103 of the tubularextension 105 of the burner 102). Preferably one or both of the heightof the stem portion 510 (in a radial direction) and the length of thehook portion 520 (in a circumferential direction) can gradually decreasein a direction toward the heat source.

The lifting flights 500 of adjacent circumferential bands of insulatorflights 310 are preferably aligned in a longitudinal direction suchthat, together, they form a plurality of contiguous longitudinal liftingflights 500 (e.g., 9). The configuration of lifting flights 500 ofadjacent bands of insulator flights 310 can be complementary such that asmooth and continuous taper (from a larger size to a small size) isformed in the stem and/or hook portions 510, 520 of the lifting fights500 from an end furthest from the heat source to an end closest to theheat source. Specifically, the height and length of the stem and hookportions 510, 520 of abutting portions of adjacent lighting flights 500can have generally the same size and shape such that a smooth transitionis formed between the adjacent lifting flights 500.

Insulator flights 310 may have a number of operational advantages. Forexample, they may maximize radiant heat transfer to the aggregate andmay allow radiant energy to penetrate deep into the aggregate. Thermalenergy of the insulator flights may be conducted to the aggregate incontact with the steel surface. As a result, aggregate surface moisturemay be dried more quickly, minimizing temperature increase of asphaltcoating on RAP particles. Robust energy transfer by radiation andconduction may lower temperature of combustion gases passing through thedryer to the opposite end. This may advantageously minimizevolatilization of hydrocarbons from asphalt coated ingredients.

Insulator flights 310 may also serve to protect the dryer from prematureaging due to high heat and wear, although not limited thereto.Accordingly, they may be placed throughout a dryer (e.g., more than thecombustion zone). When placed throughout a dryer the compressed ceramicinsulation reduces heat loss through the dryer shell, improving overallthermal efficiency of entire plant rendering delicate externalinsulation unnecessary. The insulator flights 310 and lifting flights500 may help to fix the aggregate and prevent “sliding,” which increaseswear on the inside of the dryer. Insulator flights 310 can be replacedwhen worn out, saving the expense of having to replace the dryer.

Referring to FIGS. 7 & 8, the rotary dryer 300 can also include a dam530, for example at the low (i.e., downstream) end of the combustionzone, to maintain optimum depth of the aggregate independent ofproduction rate. The dam 530 can be in the form of annular wallprojecting radially inwardly from the dryer shell 320, and radiallyinwardly of the adjacent insulator flights and lifting flights, forexample about 6-8 inches. Openings or gaps 532 in the dam 530 may allowthe associated zone (e.g., the combustion zone) to empty completely whenthe feed stops, for example at the end of a production run. For example,the dam 530 can have two gaps 532 diametrically opposed from one another(e.g., 180 degrees apart). However, other numbers and configurations ofgaps are contemplated.

Referring to FIG. 9, a system and method according to the presentteachings can enable the use of a preferred pollution control systemwith 100% RAP mixes and high percentage RAP mixes (>40%). Highpercentage RAP mixes, and particularly 100% RAP, have at times beendisfavored because they can result in more hydrocarbon emissions thannon-RAP. To address this, prior systems have been developed to employindirect heating so that the small amount of hydrocarbons volatilizedduring heating may be incinerated by the indirect process heater.However these systems are thermally inefficient. The present system mayresult in less dust as compared to systems using no or a lower level ofRAP because less or no new (e.g., virgin) fine aggregate (typicallyhaving high levels of dust) may be required.

The present system can have a direct fired rotary dryer 600 followed byone or more pollution control device(s) 602 operable to treat emissionsfrom a direct fired rotary dryer 600 so that hydrocarbons andparticulates are substantially removed from the emissions before theyare released into a surrounding environment.

The pollution control device 602 can include an inertial separation zone604, followed by a cooling zone 606, which is followed by a fiber bedfilter 608. The inertial separation zone 604 is operable to removerelatively large airborne particulates from the emissions, for exampleparticulates from about 150 to about 50 microns (100 to 325 mesh). Thecooling zone 606 is operable to cool the emissions from the rotary dryer600 enough that such the emissions achieve a temperature that iscompatible with the fiber bed filter 608, for example to a temperatureless than about 180 degrees Fahrenheit. The fiber bed filter 608 isconfigured to provide coalescent filtration of emissions from the rotarydryer 600. The coalescent filtration may be achieved by subjecting theemissions from the rotary dryer to Brownian diffusion filtration,although not limited thereto. Fiber bed filters suitable for use in thesystem are commercially available, for example, from Air Clear.

The system may be part of a unitized portable system for RAP. Byunitized it is meant that the pollution control 602 may be on the samechassis as the dryer 600 and heating mechanism 610 (e.g., burner).Reduced particulate emissions help to enable a compact, transportabledesign. A portable system may be preferable during the winter seasonwhen conventional plant maintenance is taking place. It may also bepreferable for remote regions with large distances between conventionalplants or where specialty contractors may require small capacity systemsto produce “make safe” material.

In the portable unitized system, the dryer may be either parallel orcounter flow and may have two RAP feeds as disclosed herein, and theburner may be direct fired or external. The pollution control maycomprise a fiber bed coalescing filter, which may include disposableparticulate filter media and/or adiabatic cooling water spray.

While the present teachings have been described above in terms ofspecific embodiments, it is to be understood that they are not limitedto these disclosed embodiments. Many modifications and other embodimentswill come to mind to those skilled in the art to which this pertains,and which are intended to be and are covered by both this disclosure andthe appended claims. It is intended that the scope of the presentteachings should be determined by proper interpretation and constructionof the appended claims and their legal equivalents, as understood bythose of skill in the art relying upon the disclosure in thisspecification and the attached drawings.

What is claimed is:
 1. A method of manufacturing asphalt using recycledasphalt coated aggregate (RAP), comprising: providing a rotary dryerhaving a first end and a second end, and a material stream flow towardthe second end; a burner operable to heat the rotary dryer and materialtherein, and to create a maximum gas temperature inside a volume of therotary dryer at a location between the first and second ends, a firstinlet upstream of the location of the maximum temperature, a secondinlet downstream of the location of the maximum temperature, and anoutlet adjacent the second end of the rotary dryer; selecting a firstaggregate and a second aggregate, the first aggregate being at leastprimarily coarse aggregate and the second aggregate being at leastprimarily fine RAP; operating the rotary dryer and during the operationintroducing the first aggregate into the rotary dryer at the firstinlet, introducing the second aggregate into the rotary dryer at thesecond inlet, and heating and mixing the first and second aggregatesforming a mixture; and outputting the mixture from the rotary dryer atthe outlet.
 2. The method of claim 1, wherein the first aggregate is atleast primarily coarse RAP.
 3. The method of claim 1, wherein the secondaggregate consists essentially of fine RAP.
 4. The method of claim 3,wherein the first aggregate is at least primarily coarse RAP.
 5. Themethod of claim 4, wherein the first aggregate consists essentially ofcoarse RAP.
 6. The method of claim 5, wherein the second aggregateconsists of fine RAP.
 7. The method of claim 6, wherein the firstaggregate consists of coarse RAP.
 8. The method of claim 1, wherein:only coarse RAP is introduced into the rotary dryer at the first inlet;and only fine RAP is introduced into the rotary dryer at the secondinlet.
 9. The method of claim 1, further comprising: providing the firstinlet adjacent the first end of the rotary dryer, and the firstaggregate being at least primarily coarse virgin aggregate; providing athird inlet between the first inlet and the location of the maximumtemperature; selecting a third aggregate, the third aggregate being atleast primarily coarse RAP; and during the operation, introducing thethird aggregate into the rotary dryer at the third inlet.
 10. The methodof claim 9, wherein the second aggregate consists essentially of fineRAP.
 11. The method of claim 9, wherein the third aggregate consistsessentially of coarse RAP.
 12. The method of claim 9, wherein the firstaggregate consists essentially of coarse virgin aggregate.
 13. Themethod of claim 9 wherein the second aggregate consists of fine RAP. 14.The method of claim 9, wherein the third aggregate consists of coarseRAP.
 15. The method of claim 9, wherein the first aggregate consists ofcoarse virgin aggregate.
 16. The method of claim 9, wherein only virginaggregate is introduced into the rotary dryer at the first inlet; andonly RAP is introduced into the rotary dryer at the second and thirdinlets.
 17. The method of claim 16, wherein only fine RAP is introducedinto the rotary dryer at the second inlet; and only coarse RAP isintroduced into the rotary dryer at the third inlet.
 18. The method ofclaim 9, wherein coarse RAP aggregate comprises approximately 55% to 75%of a total RAP content in the mixture, and fine RAP aggregate comprisesapproximately 25% to 45% of the total RAP content in the mixture. 19.The method of claim 1, wherein the mixture comprises at least 40% RAP.20. The method of claim 1, wherein the mixture comprises at least 75%RAP.
 21. The method of claim 1, wherein the mixture comprises at least95% RAP.
 22. The method of claim 1, wherein the rotary dryer comprises acounter flow dryer.
 23. The method of claim 1, wherein the rotary dryeris in a continuous mix plant.
 24. The method of claim 1, furthercomprising: providing a batch asphalt plant having a mixer separate fromthe rotary dryer; introducing the mixture output from the rotary dryerinto the mixer; introducing a supplemental ingredient into the mixer;and operating the mixer forming a second mixture.
 25. The method ofclaim 1, wherein the selecting comprises classifying fine aggregate asaggregate that fits through a #4 sieve and classifying coarse aggregateas aggregate that does not fit through a #4 sieve.
 26. The method ofclaim 1, wherein the selecting comprises classifying fine aggregate assands and classifying coarse aggregate as stones.
 27. The method ofclaim 1, further comprising a pollution control device having a fiberbed filter, the pollution device treating emissions from the rotarydryer.
 28. The method of claim 1, wherein the maximum temperature of therotary dryer is less than 1500 F.
 29. The method of claim 9, wherein atemperature profile of the rotary dryer defines a drying zone adjacentthe first end and having a material temperature in a range of 50-350 F;a combustion zone between the drying zone and the second end and havingan air temperature in a range of 700-1500 F; a mixing zone between thecombustion zone and the second end and having a material temperature ina range of 250-350 F; and wherein the second and third inlets arelocated in the combustion zone.
 30. The method of claim 29 wherein asupplemental ingredient is introduced into the rotary dryer in themixing zone.
 31. The method of claim 30 wherein the supplementalingredient comprises asphalt cement and/or recycling agents.
 32. Themethod of claim 1, wherein the rotary dryer has a dam at a lower end ofthe combustion zone that maintains a depth of aggregate inside therotary dryer while it rotates.
 33. The method of claim 1, furthercomprising: placing insulation on the inside of the rotary dryer; andattaching insulator flights to the rotary dryer radially inwardly of theinsulation, the insulator flights lining at least a portion of theinside of the rotary dryer.
 34. The method of claim 33, wherein theinsulator flights comprise overlapping rectangular metal segments. 35.The method of claim 33, wherein the insulation comprises ceramicinsulation.
 36. The method of claim 33, further comprising: attachinglifting flights to the insulator flights, the lifting flights beingoperable to agitate aggregate as the rotary dryer rotates.
 37. Themethod of claim 33, wherein the insulator flights are locatedsubstantially throughout the rotary dryer between the first and secondends.
 38. The method of claim 33, wherein the rotary dryer has noexternal insulation.
 39. Use of the method for manufacturing asphalt ofclaim 1 in a portable unitized mix plant.
 40. The method of claim 1,wherein the burner has a tubular extension with an end; and theproviding a second inlet comprises shortening the tubular extension sothat the second inlet is between the end of the tubular extension andthe location of the maximum temperature.
 41. The method of claim 9,wherein the providing a third inlet comprises affixing a collar to therotary dryer.